1. Field of the Invention
This invention relates to polymeric materials having luminescent metal complexes attached thereto. The invention also relates to polymeric-metal complex salts comprising at least one polymeric material having a plurality of first-type functional groups having a charge, and at least one metal complex having an opposite charge. The invention further relates to electronic devices in which the active layer includes such polymeric materials.
2. Description of the Related Art
Organic electronic devices that emit light, such as light-emitting diodes that make up displays, are present in many different kinds of electronic equipment. In all such devices, an organic active layer is sandwiched between two electrical contact layers. At least one of the electrical contact layers is light-transmitting so that light can pass through the electrical contact layer. The organic active layer emits light through the light-transmitting electrical contact layer upon application of electricity across the electrical contact layers.
It is well known to use organic electroluminescent compounds as the active component in light-emitting diodes. Simple organic molecules such as anthracene, thiadiazole derivatives, and coumarin derivatives are known to show electroluminescence. Semiconductive conjugated polymers have also been used as electroluminescent components. Polymeric materials with stilbenyl or oxadiazole side chains have been reported by Holmes et al., U.S. Pat. No. 5,653,914.
Polymeric light-emitting compounds are frequently insoluble in most common solvents and can be difficult to coat. They are also usually susceptible to degradation when exposed to air and/or moisture, which can complicate the coating process. Small molecule light-emitting materials are usually deposited by evaporative techniques. The equipment required for such processes can be quite expensive and may not be adaptable to continuous processing. Small molecule light-emitting materials can be coated from solution. However, they have a tendency to crystallize with evaporation of the coating solvent, which reduces their electroluminescent effectiveness.
There is a continuing need for electroluminescent compounds having improved efficiency and processes for preparing them.